More than one in 500 children have some form of autism, according to the Centers for Disease Control. All autistic children suffer from an impaired ability to communicate and relate to others, but some of them are able to socially interact to a greater degree than their peers. A recent study of a group of these so-called high functioning autistics suggests the neurological basis for their social impairment.

Neuroscientist Mirella Dapretto of the University of California Los Angeles and her colleagues surveyed the brains of 10 autistic children and an equal number of nonautistic children as they watched and imitated 80 different faces displaying either anger, fear, happiness, sadness or no emotion. By measuring the amount of blood flowing to certain regions of the children's brains with a magnetic resonance imaging (MRI) machine, the researchers could determine what parts of the brain were being used as the subjects completed the tasks. The autistic children differed from their peers in only one respect: each showed reduced activity in the pars opercularis of the inferior frontal gyrus--a brain region located near the temple.

This section of the brain has been shown by other studies to be part of the so-called mirror neuron system, which allows humans to understand the intentions of other human beings by observing their actions or imitating their behavior. When damaged, it can interfere with speech.

Although the high-functioning autistic children were able to imitate the facial expressions, they had trouble understanding the corresponding emotional state. The study suggests that the incompletely activated mirror neuron system is to blame. In fact, the less blood that flowed to this region of the brain in each autistic child, the less social ability that child showed--providing more support for the apparent link. The research appears in the current issue of Nature Neuroscience.